Paternity sharing in insects with female competition for nuptial gifts

Abstract Male parental investment is expected to be associated with high confidence of paternity. Studies of species with exclusive male parental care have provided support for this hypothesis because mating typically co‐occurs with each oviposition, allowing control over paternity and the allocation of care. However, in systems where males invest by feeding mates (typically arthropods), mating (and thus the investment) is separated from egg‐laying, resulting in less control over insemination, as male ejaculates compete with rival sperm stored by females, and a greater risk of investing in unrelated offspring (cuckoldry). As strong selection on males to increase paternity would compromise the fitness of all a female's other mates that make costly nutrient contributions, paternity sharing (males not excluded from siring offspring) is an expected outcome of sperm competition. Using wild‐caught females in an orthopteran and a dipteran species, in which sexually selected, ornamented females compete for male nuptial food gifts needed for successful reproduction, we examined paternity patterns and compared them with findings in other insects. We used microsatellite analysis of offspring (lifetime reproduction in the orthopteran) and stored sperm from wild‐caught females in both study species. As predicted, there was evidence of shared paternity as few males failed to sire offspring. Further support for paternity sharing is the lack of last‐male sperm precedence in our study species. Although paternity was not equal among sires, our estimates of paternity bias were similar to other insects with valuable nuptial gifts and contrasted with the finding that males are frequently excluded from siring offspring in species where males supply little more than sperm. This suggests paternity bias may be reduced in nuptial‐gift systems and may help facilitate the evolution of these paternal investments.


| INTRODUC TI ON
Although females typically invest more in offspring than males, males of some species can contribute to offspring fitness via paternal care or by feeding their mates (Gwynne, 1991(Gwynne, , 2016Janicke et al., 2016;Trivers, 1972). Paternal care, found in some fish, frogs, and birds, consists of behaviors such as nest building, brooding, feeding, or protecting offspring (Clutton-Brock, 1991). Nutritional donations provided during courtship or copulation (known as nuptial gifts) are more common in invertebrates and consist of a male's own body parts, secretions, or prey items that benefit a female and her offspring (Thornhill, 1976;reviewed in Vahed, 1998;Lewis et al., 2014). Such investments (paternal effort; Gwynne, 1984a;Thornhill, 1976) can be costly for males and limit their ability to invest in future mates (Gwynne, 1990;Trivers, 1972), yet the direct benefits to females and their offspring can lead to females competing for multiple matings (Bonduriansky, 2001;Gwynne & Simmons, 1990;Herridge et al., 2016). In some species, this competition results in strong sexual selection and the evolution of secondary sexual traits in females (Gwynne, 1981(Gwynne, , 1991(Gwynne, , 2016Gwynne & Simmons, 1990;Hare & Simmons, 2018;Herridge et al., 2016;Simmons, 1992;Thornhill, 1979;Tobias et al., 2012;Trivers, 1972).
Central to parental investment theory (Møller & Birkhead, 1993;Requena & Alonzo, 2017;Trivers, 1972;Westneat & Sherman, 1992), males that contribute to offspring are expected to have high confidence of paternity to avoid the fitness costs of cuckoldry (investment in unrelated offspring). Thus, high paternity confidence is thought to facilitate the evolution of paternal effort and investing males will be under strong selection to increase their confidence of paternity (Møller & Birkhead, 1993;Requena & Alonzo, 2017;Trivers, 1972;Westneat & Sherman, 1992). This appears to be the case in many species with paternal care, as insemination is controlled by the male and typically precedes the investment, allowing males to have high confidence in the paternity of the offspring they care for. Examples include pipefish, where unfertilized eggs are placed in an enclosed male brood pouch before undergoing a prolonged pregnancy (Jones & Avise, 2001) or when there are repeated copulations prior to each egg laid, as is the case in Abetus water bugs that rear eggs on their backs (Smith, 1979) and sequentially polyandrous birds that help care for young (Delehanty et al., 1998;Møller & Birkhead, 1991;Owens et al., 1995;Schamel et al., 2004).
In systems with nuptial gifts, however, males provide the investment during courtship or copulation (Lewis et al., 2014) and oviposition/fertilization occurs separately, resulting in less direct control over paternity and thus greater potential for cuckoldry.
When females mate with multiple males prior to oviposition (common among arthropods; Arnqvist & Nilsson, 2000;Eberhard, 1985;Simmons, 2001), paternity is achieved in competition with rival ejaculates that have been stored within a specialized sperm storage organ (Parker, 1970;Simmons, 2001). Thus, selection for paternity has led to a variety of traits that allow males to bias fertilizations in their favor (Eberhard, 1985;Lloyd, 1979;Parker, 1970;Simmons, 2001).
These traits include increased sperm quantity or motility that increases fertilization success (Parker et al., 2017;Rowe & Pruett-Jones, 2011), attractive male phenotypes that result in preferential sperm usage by the female (Albo et al., 2013;Fedina, 2007;Lüpold et al., 2013;Pizzari & Birkhead, 2000), as well as behaviors that reduce the intensity of sperm competition such as mate guarding, mating plugs, or removal of rival sperm (Birkhead, 1979;Simmons, 2001;Waage, 1979). As a result, paternity is frequently biased in favor of, for example, the highest-quality males or those that were the last to mate with a female prior to laying eggs (Birkhead & Hunter, 1990;Eberhard, 1985;Lloyd, 1979;Parker, 1970;Simmons, 2001).
Given that investing males are expected to have a high confidence of paternity, one hypothesis is that insect paternity will be highly biased when males invest in nutritious nuptial gifts, possibly via last male sperm precedence due to its prevalence in insects (Gwynne, 1984a;Simmons, 2001). On the other hand, while such biased paternity benefits the successful males, it results in cuckoldry for all other mating males who have also invested substantially in a female's offspring (Good et al., 2006) and may not be able to mate again for several days (Gwynne, 1990;Perry & Tse, 2013).
Thus, an alternative hypothesis to that of highly biased paternity is that sperm competition results in little paternity bias (i.e., a "fair raffle" due to sperm mixing and/or female control; Parker, 1990;Simmons, 2001). As this would result in each male siring a portion of a female's brood, it may allow sufficient paternity confidence to facilitate the evolution of male nutritional investments in offspring (Sakaluk, 1986). In addition to this, selection for sperm competition mechanisms that result in strong paternity bias such as sperm displacement or inducing female refractory periods (Simmons, 2001) is probably undermined in systems where females rely on gifts for survival or egg development as they tend to mate frequently to obtain male-supplied nutrition prior to oviposition. Under this hypothesis, we expect there to be shared or near-equal paternity rather than a strong bias in insect systems that invest in offspring via nuptial feeding.
Most sperm competition research with arthropods has focused on paternity outcomes when each female is mated to two males in the lab. However, hypotheses about relative paternity are ideally tested using matings from the wild. These studies, typically using microsatellite markers of paternity, are less common and have shown variation in fertilization patterns (Frentiu & Chenoweth, 2008;Good et al., 2006;Simmons, 2001Simmons, , 2007. In studies of species with no mate feeding, analysis of offspring from wild-caught females has revealed evidence of high paternity bias: in fruit flies (Drosophila melanogaster;Imhof et al., 1998 and Drosophila serrata;Frentiu & Chenoweth, 2008), the tobacco fly (Bactrocera cacuminata; Song et al., 2007), and several species of gryllid crickets (Gryllus bimaculatus ;Bretman & Trezenga, 2005, Telogryllus commodus, Telogryllus oceanicus; Simmons & Beveridge, 2010, and Laupala cerasina;Turnell & Shaw, 2015). In comparison, in species with mate feeding, studies suggest there is little paternity bias and no last male sperm precedence in wild-caught females, including ladybird beetles (Adalia bipunctata; Haddrill et al., 2008), a katydid (Requena verticalis;Simmons, 2007), and a fruit fly (Drosophila mojavensis; Good et al., 2006). However, for two other gift-giving katydids, Pholidoptera griseoaptera (Parker et al., 2017) and Ephippiger ephippiger , high paternity bias has been reported. The findings for these two species may be explained by the methods used to measure paternity bias. As in most other studies, Hockham et al. (2004) measured the paternity skew among successful sires ( ∑ (proportion offspring sired) 2 ; Starr, 1984) in E. ephippiger, but did not include an estimate of the number of failed inseminations (males siring no offspring), which is an important component of paternity bias (Bretman & Trezenga, 2005;Gwynne & Lorch, 2012). Although both metrics were used to assess paternity bias in P. griseoaptera, analyses were conducted only on eggs showing embryonic development (less than half a clutch) as undeveloped eggs require several winters (diapause triggers) to hatch (Hartley & Warne, 1972;Ingrisch, 1986).
In the current study, we investigate the outcome of sperm competition using wild-caught insects of two species from different orders where males provide ornamented females with valuable nuptial gifts: the long-tailed dance fly, Rhamphomyia longicauda (Diptera: Empidae) and an orthopteran ground weta, Hemiandrus pallitarsis (Orthoptera: Anostostomatidae) (Figure 1), in which we analyze relative paternity for all of a female's offspring (her lifetime reproduction). In both these species, nuptial gifts represent a paternal investment because females rely on them for successful offspring production (Browne, 2021;Downes, 1970;Gwynne, 2004;Hunter & Bussière, 2019) and appear to compete for matings, in part indicated by secondary sexual traits (Funk & Tallamy, 2000;Gwynne, 2004Gwynne, , 2005. If low paternity bias (i.e., fair raffle; Parker, 1970) helps facilitate the evolution of paternal investments by increasing confidence of paternity (i.e., reducing the chance of cuckoldry), we predict that there will be reduced paternity bias in both ground weta and dance flies, especially when compared with insect species that do not provide nuptial gifts.
Using several common metrics to measure bias, we expect to observe (1) few males excluded from fathering offspring, (2) similar paternity shares among sires, and (3) little or no evidence of lastmale sperm precedence.

| Study species
Males of New Zealand "short-tailed" ground weta provide females with spermatophylax meals consisting of gelatinous seminal secretions that are adhered to her mid-abdomen, separate from the sperm-containing ampulla (Gwynne, 2002(Gwynne, , 2004(Gwynne, , 2005. Female H. pallitarsis mate multiply to obtain these gifts (Browne, 2021), probably to help them survive a period of 5-6 months without food when they care for eggs laid in an underground brood chamber (hence their "short-tail" reduced ovipositor) before dying (Gwynne, 2004). Females that obtain more gifts (mates) produce a greater number of surviving offspring (Browne, 2021) and apparently compete for mates as they possess an "ornamental" secondary genitalic device (accessory organ: Gwynne, 2004Gwynne, , 2005. This device is inserted between two main parts of the male genitalia as the gift is deposited (Gwynne unpublished) and appears to be under sexual selection (Browne, 2021). Because ground weta females lay all their eggs following a month-long mating season (Gwynne, 2004), there is high potential for sperm competition, and we are able to measure paternity from a female's lifetime production of offspring.
Male empid dance flies, Rhamphomyia longicauda, catch prey (adults of small aquatic insects), which they transfer to females in exchange for mating within swarms (Funk & Tallamy, 2000). As females do not hunt on their own, they rely on these mating gifts to obtain protein for egg development (Downes, 1970;Hunter & Bussière, 2019) and mate multiply within a mating season (Downes, 1970;Herridge, 2016). Swarming females possess two sex-specific ornaments (pinnate scales on the legs and inflated abdominal sacs) that function in attracting prey-carrying males that are available only during swarming (Cumming, 1994;Funk & Tallamy, 2000); about an hour each dusk and dawn. Although studies have not shown directional sexual selection on females in this species (See Herridge, 2016;Wheeler et al., 2012), there is evidence that males prefer females with larger ornaments (Funk & Tallamy, 2000;Murray et al., 2018), even though ornament size correlates weakly with egg number and size (Funk & Tallamy, 2000;Wheeler, 2008). R. longicauda is well suited for testing our hypothesis, since females possess a single sclerotized sperm storage organ, in contrast to the multi-channeled structure of many other dipterans (Pitnick et al., 1999;Puniamoorthy et al., 2010), creating high potential for sperm displacement and thus biased paternity in favor of the last male (Simmons, 2001).

| Collection and rearing
At the end of the mating season, we collected 10 H. pallitarsis pairs (2017) and allowing 2-3 months for females to lay eggs, as well as an additional 5-6 months for eggs to mature. While in the brood chambers, we exposed females to typical winter temperatures, which were based on New Zealand weather records. All but three females laid eggs; however, these only developed in 19 of the broods, apparently due to female mortality. After eggs began hatching, we froze (at −20°C) the mothers and offspring (hatched nymphs or eggs with eye spots visible through the chorion) from 17 broods, excluding two broods where less than five eggs developed. We then extracted the sperm storage organ from all females, isolated the contents using >70% ethanol, which causes sperm to harden into a pellet (Tripet et al., 2001), and stored them at −20°C.
Similarly, we collected R. longicauda mating pairs (in copula,

| Paternity analysis
Because of difficulties genotyping dance fly offspring, methods of paternity analysis differed between the two species. In ground weta, we used data from 11 to 51 (mean: 28.8) offspring (95% of those collected) to estimate the number of sires in each brood (n = 17).
We first estimated the minimum sire number using GERUD 2.0 (Jones, 2005), a parentage program that computes the minimum father combination given the offspring genotypes across multiple loci. Offspring that shared an allele with a female's last mate at all loci were considered to be fathered by this male. Additionally, we estimated the most likely number of sires in each brood using COLONY Version 2.0.6.6 (Jones & Wang, 2010

| Statistical analysis
In both ground weta and dance flies, we tested whether paternity patterns deviated from a "fair raffle" scenario (Parker, 1990), in which males sire equal (or near equal; Herridge, 2016) proportions of offspring. Among the multiply mated females, we measured the paternity skew using Starr's (1984)  Finally, we tested for evidence of last-male sperm precedence in both H. pallitarsis and R. longicauda by determining whether a female's last mate fathered a greater proportion of offspring than other males, or than would be expected by equal shares. One weta brood was removed from this analysis because the last male did not appear to successfully inseminate the female, as his alleles were not found in either her offspring or stored sperm.
We estimated sire number in dance flies using the 11 broods from which we were able to genotype offspring. When we used the conservative method of allele counting, the number of sires averaged 3.6 ± 1.3 SD and ranged from 2 to 6 sires. Estimates of sire number were much higher when using COLONY, which averaged 13.5 ± 5.9 SD sires and ranged from 7 to 26. In dance flies, the number of offspring tested did influence the number of sires we were able to detect. We found a significant positive relationship between the number of offspring genotyped and number of sires detected for both of our estimates; however, this relationship was much stronger when using COLONY rather than allele counting (Allele counting: ß = .07, R 2 = .69, p = .002; COLONY: ß = .34, R 2 = .87, p = < .0001).
Regardless of the method used to estimate sire number, all females mated multiply and had offspring fertilized by at least two sires.

| Paternity bias
Additional alleles, suggestive of males that mated but did not sire offspring, were found in the sperm storage organ of five female ground weta; however, these rarely represented more than one male  For dance flies, although we could not genotype the contents of a female's sperm storage organ to estimate the proportion of failed matings, we found paternity skew among sires, similar to the weta.

| Last-male sperm precedence
In ground weta, a female's last mate did not consistently have a fertilization advantage. Based on the minimum father combination (GERUD), last males were seldom the most successful male (42% of broods) but fathered offspring in all but two broods (Figure 4a).
Overall, a female's last mate did not father a significantly greater proportion of offspring than previous males (Welch two sample t- In the dance flies, there was no evidence of last-male sperm precedence in our samples. Although last-male alleles were detected in offspring from each brood, the most likely paternal configuration (COLONY) suggested that 73% of these males did not fertilize any offspring and none sired the majority ( Figure 5). Overall, last males fathered a significantly lower proportion of offspring than previously mated males (Welch two sample t-test: t = −4.07, df = 13.58, p = .001) and that expected under a fair raffle scenario (equal shares among sires) (one-tailed paired t-test: t = −3.74, df = 10, p = .004).

| DISCUSS ION
For two insect species where sexually selected, ornamented females rely on nutrition provided by males during mating, we show evidence of multiple (shared) paternity with few males excluded from fathering offspring and no last-male advantage. While we did observe skewed paternity (unequal paternity shares) among sires, paternity bias appears to be overall lower compared with insects that do not contribute paternal effort. While each male will only sire a portion of a female's brood, we suggest that low paternity bias reduces the chance of complete paternity loss (thus increased confidence in paternity), which may facilitate the evolution of systems where all mating males make paternal investments via nuptial gifts (Sakaluk, 1986). While this is contrary to some predictions about increased paternity bias through last-male sperm precedence in species that invest in nuptial gifts (Gwynne, 1984a;Simmons, 2001), it is comparable with patterns found in many paternal care systems where females distribute their eggs between several males, each of which has high paternity confidence (Berglund et al., 1988).
In ground weta (H. pallitarsis), paternity estimates using a single brood of eggs (a female's lifetime offspring production) revealed a level of paternity confidence in which most investing males sired offspring. Although paternity was significantly skewed among sires, we found multiple paternity in most broods, with an average of 3.0 ± 1.6 SD sires (most likely estimate: 5.9 ± 2.4 SD), and no evidence of last-male sperm precedence. In dance flies (R. longicauda), multiple paternity was observed in all clutches, with offspring being shared between a high number of sires (minimum mean: 3.6, most likely mean: 13.5). Paternity was again significantly skewed among sires, but we found no evidence that this was influenced by last-male sperm precedence. Paternity estimates were constrained in dance flies due to incomplete genotypic data (Gerlach et al., 2012;Jones & Wang, 2010) and an inability to incorporate population allele frequencies into the paternal configuration (COLONY). This may help F I G U R E 3 Paternity skew among offspring of female Rhamphomyia longicauda (n = 11) plotted against the most likely number of sires (determined from microsatellite analysis of offspring; COLONY). The regression line (solid) shows the linear relationship between number of sires and observed paternity skew with 95% confidence intervals showing deviation from the null skew expected when all sires father an equal number of offspring. Size of points represents the number of offspring analyzed for each estimate of paternity skew, which has a positive effect on the number of sires detected (see main text).

F I G U R E 4
Proportion of offspring fathered by last male relative to all other competing males in Hemiandrus pallitarsis ground weta using estimates from (a) GERUD (minimum sire configuration; n = 12) and (b) COLONY (most likely sire configuration; n = 16). Data are shown relative to the proportion of offspring each male would sire if paternity shares were equal (null paternity). Similar to our results, all other reports of paternity in insects with valuable nuptial gifts, including katydids (P. griseoaptera; Parker et al., 2017, E. ephippiger;Hockham et al., 2004, and R. verticalis;Simmons, 2007) a beetle (A. bipunctata;Haddrill et al., 2008), and a fly (D. mojavensis; Good et al., 2006), found some evidence of paternity skew among successful sires. Skewed paternity has also been found in species that lack nuptial gifts and have no apparent sexual competition among females, including flies (D. melanogaster; Imhof et al., 1998, D. serrata;Frentiu & Chenoweth, 2008, and B. cacuminata;Song et al., 2007), and crickets (G. bimaculatus; Bretman & Trezenga, 2005, T. commodus, T. oceanicus;Simmons & Beveridge, 2010, and L. cerasina;Turnell & Shaw, 2015); However, one main difference appears to be the higher proportion of mating males that do not sire any offspring (paternity failure) in no-gift species relative to gift species. For example, analysis of stored sperm in gryllid crickets revealed that only 60% of a female's mates sired offspring in T. commodus, 75% in T. oceanicus (Simmons & Beveridge, 2010), 51%-66% in L. cerasina (Turnell & Shaw, 2015), and approximately 45%-85% in G. bimaculatus (when comparing sires to mating rates; Bretman & Trezenga, 2005). The probability of siring offspring was greater in at least two species (not measured in D. mojavensis; Good et al., 2006) in which females eat all (Perry & Tse, 2013) or a specialized part (spermatophylax: Gwynne, 1984b) of nutritious spermatophores. In the katydid R. verticalis, all males that inseminated a female sired offspring (Simmons, 2007), and in A. bipunctata, the number of mates did not exceed the number of sires (Haddrill et al., 2008), suggesting a low rate of paternity failure. This is similar to our findings in the ground weta, where 85%-89% of mates sire offspring, as well as the dance flies, where the number of mates (Herridge, 2016) did not exceed the number of sires.
In most insect species, some level of paternity failure may be expected due to the occurrence of infertile males or those that produce non-viable eggs (Garcia-González, 2004;Simmons & Beveridge, 2010). While these cases probably inflate the number of males that appear to be unsuccessful in sperm competition (Garcia-González, 2004, this measure is an important indicator of paternity bias (Bretman & Trezenga, 2005). In particular, cases of zero fitness are especially important in driving variation in reproductive success (sexual selection) on males (see Gwynne & Lorch, 2012;Shuster & Wade, 2003). Unfortunately, the proportion of mates that sire offspring is not commonly reported in studies of paternity, which may explain why high bias (interpreted from paternity skew alone) was reported for E. ephippiger , a katydid with extremely large spermatophylax gifts (Vahed & Gilbert, 1996). This was not the case in another gift-giving katydid species, P. griseoaptera (Parker et al., 2017), however, as analysis of stored sperm indicated high rates of paternity failure in addition to unequal paternity among sires (skew).
Notably, one reason for this finding may be the low proportion of offspring sampled, potentially underestimating the percentage of successful sires. As Pholidioptera (and also Ephippiger) require several winters for eggs laid late in the season to hatch (Hartley & Warne, 1972;Ingrisch, 1986), paternity analyses were conducted on a relatively small portion (20 per brood) of the offspring that reached the whole-embryo stage in the lab (about 40% of viable eggs). The remaining eggs, in addition to those requiring additional winters to continue development, were not included (Parker et al., 2017), potentially inflating the number of paternity-losing males (Fritzsche & Arnqvist, 2013;Gerlach et al., 2012;Imhof et al., 1998). Alternatively, high paternity bias may be less costly in this species if the male's spermatophylax gift primarily functions in maximizing sperm transfer, by extending the duration of spermatophore attachment (mating effort) rather than investment in a particular female and her offspring (Will & Sakaluk, 1994; reviewed in Vahed, 1998). Indeed, the size of the spermatophylax F I G U R E 5 Proportion of offspring fathered by last male relative to other siring males in Rhamphomyia longicauda dance flies (using COLONY to estimate the most likely sire configuration; n = 11). Data are shown relative to the proportion of offspring each male would sire if paternity shares were equal (the null).
gift is small in P. griseoaptera (7% of his body weight) relative to some other katydids (Vahed & Gilbert, 1996), and male refractory periods are shorter than those of females (Parker et al., 2017).
Despite the low rate of paternity failure, there was significant paternity skew among sires in our species, which is consistent with findings in other insects regardless of whether they donate nuptial gifts. The observed paternity skew in our study did not appear to be related to last-male sperm precedence (common in insects; Simmons, 2001). We note, however, that in the dance flies, our collection methods (mating pairs in flight) may have reduced copulation duration and thus the degree of sperm transfer from a female's last mate. This unlikely to be an issue in the ground weta as mated pairs were collected at the end of copulation when the female had nearly finished consuming the spermatophylax gift. The large, elastic sac of the sperm storage organ of ensiferan Orthoptera such as ground weta likely facilitates sperm mixing, even with frequent mating (Simmons, 2001). In contrast, dance flies have a sclerotized, non-flexible sperm storage organ that would be expected to cause sperm displacement, with sperm from previous males being indirectly flushed from the storage organ (Simmons, 2001). Indeed, Herridge (2016) found that stored sperm tended to be dominated by a particular male in R. longicauda, but this could not be connected to mating order or the resulting paternity shares. Given the lack of last-male sperm precedence, there are several possibilities that may explain the occurrence of paternity skew in our species, despite the prediction of reduced bias. First, random error during fertilization (e.g., slow or "sloppy" sperm mixing or sperm loss; Simmons, 2001) is likely to cause small differences in paternity success among males that results in deviation from a perfect fair raffle (Herridge, 2016). Thus, while the observed skew was significant in both the ground weta and dance fly, this may not represent much more bias than would be expected at under a "noisy fair raffle" scenario (Herridge, 2016). Alternatively, the observed skew could be caused by differences in male phenotype related to variation in sperm viability (Garcia-González, 2004 or the number of sperm transferred (Parker et al., 2017;Simmons, 2001).
In particular, gift size or quality may be expected to play a role in fertilization success by increasing copulation duration (reviewed in Vahed & Gilbert, 1996;Haddrill et al., 2008;Vahed, 1998) or influencing patterns of sperm storage by the female (Albo et al., 2013;Engels & Sauer, 2006;Fedina, 2007). Because the spermatophylax is secreted by the male's accessory glands, variation in ground weta gift quality is expected to be mediated by differences in physiological condition (reviewed in Lewis et al., 2014). Despite this, preliminary evidence suggests that male size (indicator of condition; Emlen, 1997;Emlen et al., 2012;Johnstone et al., 2009) does not influence the number of offspring sired in H. pallitarsis (unpublished data). Differences in copulation duration may be expected in ground weta, however, since sperm transfer ends in ensiferan Orthoptera when the externally placed sperm ampulla (Brown & Gwynne, 1997) is removed. As male short-tailed ground weta guard the female while she consumes the spermatophylax gift, this may reduce the incidence of premature removal by their mates after copulation (Gwynne, 2004). On the other hand, mating gifts in dance flies consist of prey items (usually small insects) captured by the male (Cumming, 1994;Downes, 1970). As males provide females with a diversity of different prey-types and sometimes even consume parts of the gift before entering mating swarms (as in Rhamphomyia sulcata; LeBas et al., 2004), dance fly gifts have the potential to vary considerably in protein content or handling times for the female. This may allow greater variation in gift quality and male effort relative to weta and may be expected to influence paternity by affecting the duration of female feeding and thus the amount of sperm transferred.
While paternity sharing in our two study species reduces the maximum number of offspring that can be sired by individual males, it appears to assure some paternity, as the chance of siring no offspring is low. Thus, reduced paternity bias may be an important factor in the evolution of nutritious nuptial gifts (Sakaluk, 1986). Low levels of paternity bias may be expected in other species where females rely on costly mating gifts to produce offspring such as many katydids (Gwynne, 1981(Gwynne, , 1984c(Gwynne, , 1985(Gwynne, , 1988Simmons & Bailey, 1990) and other species of empidine dance flies (Diptera: Empididae; Bussière et al., 2008;Cumming, 1994;Downes, 1970;Murray et al., 2018;Wheeler et al., 2012). writing -original draft (supporting); writing -review and editing (equal).

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are openly available in Dryad at https://doi.org/10.5061/dryad.nk98s f7wq.